An advance in the art of using halogens for disinfecting water was provided by the development of demand bactericides composed of anion exchange resins with polyiodide ions (I.sub.3.sup.-) and/or pentaiodide (I.sub.5.sup.-) at the ion exchange sites. (See, for example, U.S. Pat. Nos. 3,817,860, 3,923,665, 4,137,183, 4,190,529, 4,238,477 and 4,999,190). Such resins containing pentaiodide are capable of killing both Gram-Positive and Gram-Negative bacteria in water thereby functioning as broad spectrum bactericides, and also inactivating RNA and DNA viruses, as well as water borne Giardia cysts. [See Lambert et al., Ind. Eng. Chem. Prod. Res. Dev. (1990) 19:256-258; Fina et al., Appl. Environ. Microbiol. (1982) 44:1370-1373; and Marchin et al., Appl. Environ. Microbiol. (1983) 46:965-969.]
In the use of anion exchange resins containing polyiodide, pentaiodide or mixtures thereof, relatively insignificant amounts of iodine (or other oxidizing forms thereof) are released into the water. However, when the ion exchange sites are reduced to the iodide (I.sup.-) form, the iodide can exchange with other anions in the water. This results in the release of iodide ions into the treated water. While iodide has a very low level of toxicity, it is a physiologically active form of iodine. Government regulatory agencies may therefore be concerned with the presence of iodide in treated water.
When halogen had been used to disinfect water, it has been proposed to scavenge the residual halogen by a secondary resin treatment. For example, as disclosed is U.S. Pat. No. 3,316,173, water may be treated with bromine released from a strong base anion exchange resin. The bromine eluted from the resin in the treated water can be scavenged as described in U.S. Pat. No. 3,462,363 through use of a scavenger resin in tandem with the bromine-providing resin.
It is known that peroxides of polyvalent metals such as zirconium, titanium, lanthanium, and thorium can oxidize iodide in aqueous solution to elemental iodine: Gantz and Lambert, J. Phys. Chem. (1957) 61:112-113. These authors reported that zirconium peroxide can be formed from zirconyl ion attached to filter paper or starch. Zirconyl ion solutions were found to react irreversibly with cellulose. It was hypothesized that this was the result of the attachment of the zirconyl ion through hydroxy groups of the glucose units. After attachment of the zirconyl ions, treatment of the filter paper with hydrogen peroxide produced zirconyl peroxide which remained attached to the paper. cl SUMMARY OF INVENTION
This invention is based in part on the discovery of a novel water treating resin which is capable of oxidizing iodide to iodine and also of retaining the formed iodine. The composition comprises porous granules of a metal chelating resin which provide functional groups capable of binding polyvalent metal ions. The granules are prepared so that they contain strongly bonded zirconium peroxide. When water containing iodide is contacted with the resin, iodide is oxidized within the granules to form iodine. The iodine thus formed tends to be retained within the granules. Treated water can be produced which is essentially free of both iodide and iodine.
This invention also involves a method of treating water with the oxidizing resin described above. This method can be used for treating water which has been disinfected by being contacted with a polyiodide anion exchange resin, which results in the release of iodide ions in the treated water. The iodide-containing water is contacted with the zirconium peroxide containing chelated resin granules. The oxidizing action of the zirconium peroxide converts the iodide to iodine which is retained within the granules. By separation of the treated water from the granules, disinfected water is produced which is free of both iodide and iodine.
In preferred embodiments of the oxidizing resin of this invention, the zirconium is so strongly held that it can be repeatedly regenerated while remaining attached to the resin. The oxidative capacity of the resin can be restored by treating the resin with hydrogen peroxide, thereby making it possible to repeatedly regenerate the resin after its oxidizing capacity has been exhausted. This is an important and surprising feature of the present invention. In another application of the present invention, low concentrations of iodide in brine waters can be converted to iodine which becomes trapped in the resin matrix. Upon becoming saturated with the iodine, it can be eluted by an organic solvent such as acetone.